colorectal cancer
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What is colorectal cancer?
Colorectal cancer is a disease marked by the uncontrolled growth of cells in the large intestine (colon) or rectum (the colon's terminal portion). It is also referred to as bowel cancer or rectal cancer.
Most colorectal cancers (about 95%) are adenocarcinomas, which arise from the glandular cells in the colon wall. While the exact causes are not fully understood, genetics, age, chronic bowel diseases, a high-fat diet, physical inactivity, and certain gut bacteria can increase the risk of developing colorectal cancer. Symptoms include changes in bowel habits, blood in the stool, abdominal pain, and fatigue.
Treatment options include surgery, radiation, and/or chemotherapy. Early detection is key to preventing advanced colorectal cancer.
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Where does colorectal cancer start in the body?
Colorectal cancer starts in the large intestine (colon) or rectum. It is characterized by the uncontrolled growth of cells within these areas. Colorectal cancer typically develops slowly and can spread to surrounding and distant tissues if not detected early.
Most colorectal cancers, around 95 percent, originate in the glandular cells of the colon wall and are classified as adenocarcinomas. However, colorectal cancers may also arise in hormone-producing cells, immune cells, or the underlying connective tissue.
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What are common symptoms of colorectal cancer?
Colorectal cancer, affecting the colon or rectum, often presents with symptoms related to digestion and elimination. These include persistent diarrhea or constipation, blood in the stool, rectal bleeding, abdominal pain, loss of appetite, and fatigue. Because these symptoms can indicate various illnesses, consulting a physician for diagnosis is crucial. Risk factors include age (90% of cases are in those over 50), family history of colorectal cancer, inflammatory bowel diseases, inactivity, and high-fat diets. Symptoms can be variable, with blood in the stools as a key indicator, sometimes detectable only through chemical testing.
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How can doctors find or diagnose colorectal cancer?
Doctors use several techniques to diagnose colorectal cancer. These include a digital rectal exam, where a doctor feels the rectum for abnormalities, and a fecal immunochemical test (FIT), an at-home test for detecting blood in the stool.
If colorectal cancer is suspected, further screening may be done via colonoscopy, where the entire colon is examined with a flexible tube. A sigmoidoscopy uses a similar device to examine the rectum and end of the colon. Doctors may also perform a biopsy, removing tissue for microscopic examination, or use imaging techniques like MRI, CT scans, or rectal ultrasound to check for metastasis. An X-ray procedure, called a double-contrast barium enema, may also be used.
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What are some risk factors for developing colorectal cancer?
Several factors can increase the risk of developing colorectal cancer. Age is a significant factor, with 90% of cases diagnosed in people over 50, but it can also occur in younger individuals. A family history of colorectal cancer, such as familial adenomatous polyposis (FAP), Gardner syndrome, and hereditary nonpolyposis colon cancer (HNPCC), can predispose individuals to the disease.
Other risk factors include chronic inflammatory bowel diseases like Crohn's disease or ulcerative colitis, a high number of noncancerous polyps, physical inactivity, and a diet high in fats. Certain gut bacteria, such as Fusobacterium, have also been implicated. High alcohol consumption and low intakes of calcium and folic acid have been linked to increased rates of colorectal cancer. Consumption of red and processed meats may also increase the risk. Obesity is a risk factor in men and premenopausal women, while physical activity is associated with a decreased risk.
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How is colorectal cancer usually treated?
Colorectal cancer treatments include surgery, chemotherapy, and radiation, with the specific approach depending on the cancer's location and spread. Localized cancers in the colon or rectum typically require surgery. Early-stage colon cancer can be removed via colonoscope, while other early cancers necessitate surgical resection of the cancerous section, surrounding tissue, and nearby lymph nodes.
Rectal cancers may be treated by removing cancerous polyps, surrounding tissues, or larger sections of the rectum, sometimes using electrofulguration. If the lower rectum is affected, a colostomy might be necessary. If the cancer has spread, more extensive surgery may be needed to remove affected tissues in the uterus, prostate, liver, kidneys, or bladder. Radiation, using external beams or implanted radioactive pellets, is often used alongside surgery to shrink tumors or eliminate remaining cancerous tissue. Chemotherapy is also an option, particularly for cancers that have spread, and as an adjuvant therapy to surgery and radiation.
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colorectal cancer, disease characterized by uncontrolled growth of cells within the large intestine (colon) or rectum (terminal portion of the large intestine). Colon cancer (or bowel cancer) and rectal cancer are sometimes referred to separately. Colorectal cancer develops slowly but can spread to surrounding and distant tissues of the body.
Causes and symptoms
Like most cancers, colorectal cancers have multiple causes, many of which remain unknown. Some cases appear to be inherited, while others seem to occur randomly or to have nongenetic causes. Approximately 95 percent of colorectal cancers involve the glandular cells in the wall of the colon and are called adenocarcinomas (see carcinoma). Other colorectal cancers may begin among hormone-producing cells, immune cells, or underlying connective tissue.
Several factors increase the risk of developing the disease. In general, colorectal cancer becomes more common with increasing age; 90 percent of cases are diagnosed in people age 50 or older. However, the malignancy also occurs with some frequency among persons under age 50. A family history of colorectal cancer—specifically, forms such as familial adenomatous polyposis (FAP), Gardner syndrome, and hereditary nonpolyposis colon cancer (HNPCC)—can predispose an individual to developing colorectal cancer. Each of these conditions is caused in part by a known genetic mutation. In addition, Ashkenazi Jews have a slightly higher incidence of colorectal cancer due to a mutated gene, and there exists a gene mutation that increases risk of colorectal cancer in people of European descent but does not increase risk in people of Japanese descent. This latter mutation, discovered in 2008, was the first to provide evidence of ethnic differences in genetic susceptibility to colorectal cancer.
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Chronic inflammatory bowel diseases such as Crohn disease or ulcerative colitis are associated with colorectal cancer, as is the presence of a large number of noncancerous polyps along the wall of the colon or rectum. Other risk factors include physical inactivity and a diet high in fats. Those who have previously been treated for colorectal cancer are also at increased risk of recurrence. Certain gut bacteria, including species of Fusobacterium, have been implicated in colorectal cancer; Fusobacterium are present at increased levels in colorectal cancer patients and can trigger inflammatory responses associated with tumour growth and progression.
Because colorectal cancer is a disease of the digestive tract, many of the symptoms are associated with abnormal digestion and elimination. Symptoms include episodes of diarrhea or constipation that extend for days, blood in the stool, rectal bleeding, jaundice, abdominal pain, loss of appetite, and fatigue. Because these symptoms accompany a variety of different illnesses, a physician should be consulted to determine their cause.
Diagnosis
Diagnoses of colon and rectal cancers are made by means of several techniques. During a digital rectal exam, the physician inserts a gloved finger into the rectum and feels its surface for abnormalities. A fecal immunochemical test (FIT) may also be used to detect the presence of blood in the stool. FIT tests can be completed at home and then mailed to a laboratory for testing. Results are sent to the patient’s physician. If colorectal cancer is suspected, the patient may undergo further screening with a procedure known as a colonoscopy.
In order to examine the rectum more carefully, a physician may use a narrow, flexible tube called a sigmoidoscope to look at the lining of the rectum and the end of the colon. Colonoscopy uses a similar device to examine the entire colon. A biopsy may also be conducted in which abnormal tissue is removed by using the colonoscope and then examined under a microscope for signs of cancer. An X-ray procedure called a double-contrast barium enema may be used. Barium sulfate is used to coat the colon, and the colon is filled with air. A series of X rays are then taken, and the resulting high-contrast images indicate any abnormalities present.
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If cancer is found, the degree to which it has spread (metastasized) from the colon or rectum is determined. Biopsies may be conducted of surrounding tissues, or one of several imaging techniques may be used to detect metastasis. Techniques include rectal ultrasound, magnetic resonance imaging (MRI), and X-ray or computed tomography (CT) scans.
Once colorectal cancer has been diagnosed, its stage is then determined to indicate how far the cancer has progressed. Stage 0 colorectal cancer is also called carcinoma in situ and is confined to the lining of the colon or rectum. Stage I cancers have spread into the connective tissue beneath the lining or into the underlying muscle layer. Stage II cancers have spread completely through the wall of the colon or rectum but have not invaded nearby lymph nodes. Stage III colorectal cancer has reached nearby lymph nodes, and stage IV cancers have spread to distant structures such as the lungs, liver, bones, or reproductive organs.
Colorectal cancer patients have an excellent five-year survival rate when the disease is detected early, and those who reach this stage often go on to live long, healthy lives. Approximately two-thirds of patients with local metastases survive for five or more years, but in cases where cancer is detected late and has spread to distant regions of the body, the five-year survival rate is very low.
Treatment
Colorectal cancer is treated by surgery, chemotherapy, or radiation. The method used depends on the site of the cancer and the degree to which it has spread. For cancers localized to the colon or rectum, surgery is usually all that is required. For early-stage colon cancer, a colonoscope may be used to remove the cancerous tissue. Other early cancers require a surgical resection, whereby the portion of the colon containing the cancerous tissue is removed along with surrounding tissue and nearby lymph nodes and the remainder of the colon is repaired.
Rectal cancers may be treated by removing only the cancerous polyp or polyps, the cancer plus surrounding tissues, or larger sections of the rectum. Some cancers may be removed by burning them in a procedure called electrofulguration. In cases where the lower portion of the rectum is involved, a colostomy may be required, whereby the surgeon creates an artificial opening for the removal of waste. If colorectal cancer has spread to surrounding tissues such as those of the uterus, prostate, liver, kidneys, or bladder, more extensive surgery may be required to remove all or part of these organs.
Both colon and rectal cancers may be treated with radiation, using either external beams or surgically implanted radioactive pellets. Radiation is usually used in conjunction with surgery—either before the surgery to shrink tumours or following surgery to destroy small amounts of remaining cancerous tissue. Chemotherapy may also be indicated for treatment of colorectal cancers, especially when cancer has spread to other parts of the body but also as an adjuvant therapy to primary surgery and radiation. Side effects of both radiation and chemotherapy may include vomiting, diarrhea, and fatigue.
Prevention
A lifestyle that includes regular exercise and a diet low in fats and high in fibre helps to prevent colorectal cancer. Early detection is important in preventing the development of advanced colorectal cancer. Some medical societies recommend regular screening by a physician after the age of 50.
Multiple studies have shown that the pain-reliever aspirin can effectively lower the risk for colorectal cancer in some persons and even reduce mortality rates for those already diagnosed with the disease. A report published in 2010 that analyzed data on aspirin use and cancer risk in different study groups over a 20-year period revealed that consistent use of low-dose aspirin (75–300 mg) lowered the risk for colon (bowel) cancer by as much as 25 percent. Long-term use of low-dose aspirin was also associated with a significant reduction in mortality from this form of the disease.